1. Technical Field
This invention relates to a sintered ferro alloy utilized in parts which require high heat and wear resistance at high temperatures. Specifically, this invention relates to a sintered ferro alloy as utilized in the valve seats or the valve faces of internal combustion engines in automotive vehicles.
2. Background Art
These days, the demand for higher speed and greater power from automotive internal combustion engines is greater than ever. Consequently, the wearing of valve parts of internal combustion becomes a more and more significant problem. Specifically, high endurance of the valve seats installed at the intake and the exhaust portions of the engine become necessary because the inner portions of the engine operate at such high temperatures.
Generally, a valve seat is subjected to high temperatures, and is struck at high speed, therefore it is necessary for a valve seat to have excellent heat and wear resistance, pitting resistance, and precise mating with corresponding parts such as valve faces.
In view of the aforementioned background, inventors of the present invention have already disclosed a ferro alloy for utilization in internal combustion engines in Japanese Patent First Publication No. 63-109142. In this alloy, amounts of carbide microparticles, borides and/or borides containing carbon are dispersed uniformly into an Fe matrix. Also rare earth elements such as La, Ce, Nd are dispersed in the matrix.
This ferro alloy has components as follows; 7 to 25 wt % of one or two elements selected from Mo and W, 2 to 10 wt % of Cr, 0.1 to 0.9 wt % of Si, less than or equal to 0.7 wt % of Mn, less than or equal to 0.05 wt % of P, 0.5 to 2.0 wt % of C, 0.5 to 2.0 wt % of B, 0.1 to 5 wt % of at least one element selected from rare earth elements such as La, Ce, Nd, Sm' Eu, Gd, Yb, Y, Sc and/or 0.3 to 7 wt % of at least one compounds selected from oxides of rare- earth elements-- such as La, Ce, Nd, Sm, Eu, Gd, Yb, Y, Sc, and if necessary, has less than or equal to 20 wt % of at least one element selected from V, Nb, Ta, Ti, Zr, Hf, Co, Ni, and residual Fe and contaminants in order to obtain desired composition.
The ferro alloy previously mentioned has good resistance to heating and wearing, and has a high degree of hardness to resist deforming to insure a good fit with corresponding parts such as valve faces. But further strength is required in this kind of ferro alloy.
Therefore, it is the object of the present invention to provide a sintered ferro alloy which can be used for valve seats in internal combustion engines having further resistance to heating and wearing.